Seismic structure orientation, such as dip and azimuth features, has broad applications, including for structure orientated smoothing as described by Fehmers, G. C. and Hocker, C. F. W., “Fast Structural Interpretation with Structure-Oriented Filtering”, Geophysics, Vol. 68, 2003, pp. 1286-1293; and for dip-steered coherence and curvature attributes as described by Al-Dossary, S., “3-D Volumetric Multispectral Estimates of Reflector Curvature and Rotation”, Ph.D. thesis, University of Houston, 2003. Structure orientation itself provides stratigraphic and geographic information for seismic data processing and interpretation.
Dip and azimuth can be computed from seismic records without picking horizons, and the results are referred to as volumetric structure orientation. Several methods have been proposed to perform the task. A slant-stack approach that searches for the most coherent direction is intuitive, as described in Luo Y., W. G. Higgs, and W. S. Kowalik, “Edge Detection and Stratigraphic Analysis Using 3-D Seismic Data”, 66th Ann. Int'l. Mtg., Soc. Expl. Geophys, expanded Abstracts, 1996, pp. 324-327. Frequency domain algorithms are also adopted in practice as described in Marfurt, K. and Kirlin, R., “3-D Broad-Band Estimates of Reflector Dip and Amplitude”, Geophysics, Vol. 65, 2000, pp. 304-320.
Both of the above methods require relatively large data windows and suffer from a loss of resolution. The known finite difference method is straightforward, but it is a first-derivative operation and therefore is prone to amplify noise. A smoothing scheme is needed for two purposes: (a) to suppress the noise, and (b) to extract large-scale features. Although the finite difference method is straightforward, smoothing its results is not simple. Because dip and azimuth are computed through the normal direction of a wave front, there is a problem with the inversion of vectors. For example, both 0° and 180° dips are horizontal events, but their average, oriented at 90°, is vertical. In other words, normal directions cannot be taken as an average arithmetically unless some additional maneuver is performed.
Numerous attempts have been made in the prior art to improve smoothing of image data such as dips and azimuths, but with limited success. For example, U.S. Pat. Nos. 4,453,219 and 4,348,748 to Clavier et al. disclose methods which calculate dips and azimuths using multiple transducers spaced around a borehole for redundant indications of displacement using a dipmeter displacement processing technique, but the method is only applicable to well-log dipmeter data.
U.S. Pat. No. 4,638,254 to Uhri discloses an iterative process for producing a preferred geological orientation of a subsurface formation by generating original vectors representing the azimuth and dip of the measurements, converting original vectors into lineations, and vector-averaging selected unit vectors to produce a resultant vector which is used to indicate a preferred orientation of the formation. The process determines and displays the orientation of subsurface formations, but is applicable only to well-log data, and only smoothes over about five to twenty data points. It is inapplicable to the sizable sets of data points, that can include from 100 to 5,000 data points that are typical of seismic data. In addition, the disclosed process performs the computations by scanning and selecting the data points to be smoothed, but no iterative approach to processing the data points is disclosed.
U.S. Pat. No. 4,852,005 to Hepp et al. discloses a method which calculates dips and azimuths using correlation intervals to derive possible offsets, but it is only applicable to well-log data and the method uses continuity-based smoothing.
U.S. Pat. No. 5,038,378 to Chen discloses a system and method which reduce noise in seismic data by smoothing fine resistivity measurements made with a tool from inside a borehole and for detecting boundaries of features using semblance values to compute orientations.
U.S. Pat. No. 5,148,494 to Keskes discloses a system and method for image analysis for processing seismic data using traces of a seismic cross-section and processing the cross-sectional data with a predetermined binary function. Such seismic cross-sections and horizon data are displayed, but no smoothing of dips and azimuths is performed.
U.S. Pat. No. 5,191,526 to Laster et al. discloses a system and method which reduce noise in seismic data using Fast Fourier Transform methods in the frequency domain, and using an f-k filter technique, but no smoothing of image data such as dips and azimuths is performed.
U.S. Pat. No. 5,299,128 to Antoine discloses a system and method which reduce noise in seismic data using resistivity measurements of a sector of a borehole wall, but the application is limited to borehole data.
U.S. Pat. No. 5,588,032 to Johnson et al. discloses an inversion method for rapid real time imaging by processing data derived from wavefield energy transmitted and scattered by an object. Inverse scattering image processing is performed, but no smoothing of image data such as dips and azimuths is performed.
U.S. Pat. No. 6,018,498 to Neff et al. discloses a method for smoothing dips and azimuths by automatically picking faults in a recorded three-dimensional seismic trace data volume. Scanning of image data, for example, using test planes is used to determine the orientation of faults, but no smoothing of image data such as dips and azimuths is performed.
U.S. Pat. No. 6,516,274 to Cheng et al. discloses a method which calculates dips and azimuths by identification of structural and stratigraphic discontinuities using cross-correlations, but no smoothing of image data such as dips and azimuths is performed.
U.S. Pat. Nos. 6,675,097 to Routh et al. and 6,993,433 to Chavarria et al. disclose an inversion method using measurements of components of potential field data at a plurality of locations over a region of interest for analyzing gravity and magnetic measurement data, rather of seismic data.
U.S. Pat. No. 6,850,864 to Gillard et al. discloses a system and method which calculate dips and azimuths using a horizontal gradient in a seismic data volume. Gradients are only computed using simple finite difference methods, and no smoothing of seismic data is performed.
Patent publication number US 2002/0022930 and U.S. Pat. No. 6,473,697 to Bouts et al. disclose a method for smoothing dips and azimuths using a local orientation of the seismic data and determining an edge in a neighborhood of a voxel. Cross-correlations or semblance values are used, but no smoothing of image data such as dips and azimuths is performed.
Patent publication number US 2005/0222774 to Dulac et al. discloses a method for smoothing dips and azimuths using digital modeling and calculating an optimal offset of data. Structurally-orientated smoothing is performed, but dips and azimuths are computed using cross-correlation methods.
Patent publication number US 2006/0122780 to Cohen et al. discloses a system and method for image analysis for processing seismic data for the identification of subterranean faults by computing three dimensional orientation of a subsurface using previously known computational methods such as Fourier transform methods.
It is therefore an object of this invention to provide a system and method for smoothing dips and azimuths that are capable of processing large volumes of data to suppress noise and to extract large-scale features.